?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ I??m asking for opinions on my idea that closing the horizon at each occupy station is preferable to our current procedure. I??m a lowly rod-man, sometimes transit-man, on a two or three man crew that usually, but doesn??t always, include the LPS. While working through Charles Ghilani??s ??Adjustment Computations?, 6th ed, I came across an example application of least squares to the conditional constraint of closed horizon. With a little help from wxMaxima I reworked Ghilani??s three-angle example to the simple case of one forward direct turn to the foresight followed by one turn from foresight to backsight.
?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ We are more ??old timey? or low budget, if you prefer, than most I read of here, relying on used, 5? total stations, no electronic data collection and ancient Carlson software. The boss is a very good, well respected surveyor, deeply knowledgeable in property law and committed to keeping costs down for his clients. We routinely shoot distances once and angles only twice. I??m proposing a revised procedure where we close the horizon by turning both angles, summing them, and adding half the error ((360-sum)/2) to the already-measured forward angle. Algebraically and mathematically, that is equivalent to computing a second estimate of the forward angle from (360-reverse_angle) and averaging the two separate estimates. It offers, however, three benefits: 1) Immediate blunder detection ?? any major difference from 360 is sure evidence of some problem that can be corrected on the spot. [I??ll forever carry the shame that I once recorded in a field book, twice, the same, identical, wrong-by-degrees angle.] ?ÿ2) Provides an idea of the total error of the two combined angles. 3) Addition is slightly simpler than subtraction and, maybe, prone to fewer mistakes under field conditions.
?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ Does this dog hunt?
More redundancy is always good in land measurement.?ÿ Redundancy provides good double-check on the measurement and well as taking that much more precision-increase.?ÿ Closing the horizon (arguably) is as good of a method as any for angles.?ÿ Depending on how the gun works, there might be other methods that are just as acceptable.?ÿ I would advise measuring distances both ways as well.?ÿ I hope you do.?ÿ (measure to the foresight and leave a prism when you move forward to measure back.)?ÿ Point out to the boss that the added precautions don't add a lot more time, and save a great deal of time if you have to come back out and remeasure.?ÿ Compared to the amount of time it takes to pick out your traverse points, set some kind of monument in the ground set up your instrument, and set up something at both back and fore-sights etc.....taking a little extra time while your leveled up and over the point is a very good bang for the buck.
PentaxBob,?ÿ?ÿsaid?ÿ "I??m proposing a revised procedure where we close the horizon by turning both angles".
Why don't you proposed buying a data collector??ÿThis way your crew can record multiple angles & distances in less time, and eliminate blunders. The time and errors saved will easily pay for itself.
More redundancy is always good in land measurement.?ÿ?ÿ
Redundancy is ignorance in reverse (someone - possible Nearly Normal - posted that years ago)
As said, get a data collector if you don't have one now.?ÿ Even an old HP DC with TDS would do the trick.?ÿ As far as just collecting data, not much has really changed in the DC programs from what we used 25 years ago.?ÿ
Closing the horizon is good for spur points, to show that a mistake wasn't made.?ÿ I wouldn't do it for traversing, though.?ÿ Doubling angles on a traverse takes insignificantly more time than just turning single angles, and it's definitely worth doing.?ÿ Closing the horizon would add a bit more time, without really doing that much more for your overall accuracy and closure.
Not sure what "ancient" Carlson software you're using, but if it's not 2004 or newer, I'd consider talking to the boss about getting at least the ICAD version for only $1750, it's worth it.
I disagree that addition is easier than subtraction.?ÿ It causes more errors.
In fact it's TOO EASY and we all make our most mistakes adding.
There is no method of checking addition except to add it up again, from the top or bottom.
Subtraction has a built-in check by adding the answer to the number subtracted to get the number subtracted from.
All other computations seem to have a built-in check too.
(Somebody slap my wrist for not knowing which number is the subtrahend and which the minuend and whatever the third one is!)
The choice of horizon versus double should be driven primarily by the type of instrument. I set more initial subdivision control with horizon closure on a wild 1500 than I care to remember. Always incredibly tight...
I use ancient Carlson software "Surveyor1" and it is actually the same basic cogo program in the bowels of the latest version of Carlson without the bells and whistles of Windows magic.
It is also one of the best cogo programs ever distrubuted to surveyors.
Doubling angles is the best and can be direcly input into your computations.
Backsite, turn angle and read - Flop scope, Backsite, turn angle and read and continue till satisfied.
I have added a DC and have an elecronic TS to record data and transfer into the computer, cogo and cadd.
Just remember, what you are learning with the ancient tools will enable you to understand and do things much better in your future station in surveying.
good luck
More redundancy is always good in land measurement.?ÿ?ÿ
Redundancy is ignorance in reverse (someone - possible Nearly Normal - posted that years ago)
More redundancy = less ignorance ????
You've made a damn decent run at understanding and then changing a procedure.?ÿ My hat is off to you sir and to your employer.?ÿ That being said, I disagree with your want to change the procedure.?ÿ While all of the new guns have dual axis compensators, sometimes they get bad, out of adjustment, or a host of other things.?ÿ The only way to catch it, is to flip the scope and double the angle.?ÿ If you are out of level, this will catch it where the closure of the horizon will not.
This method is an old throwback to when there were single axis wire compensators or no compensators on the instruments.?ÿ It's still a worthwhile procedure to this day.?ÿ Especially handy when setting corners and you turn the first angle, get line and distance, flip and turn the exact double and split the holes.?ÿ Double centering makes for really good control to come off of in a pinch.
?ÿ
But seriously, excellent effort on the topic.?ÿ I hope your boss reads this.
?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ?ÿ I was on here more back when it was SurveyorConnect. Seems like then you could reply to each response, but I don??t see how to do that now so here??s a combined reply.
First, thanks for all the input. Now for specifics:
Tom Adams ?? we do routinely shoot backsight distance, then turn to the foresight and record HA plus HD, VD, SD and then return to BS and turn the FS angle a second time. Then side shots or move.
Leegreen, JPH, A Harris ?? I??ve had many conversations with the boss on the merits I see in using a DC, especially a reduction in data capture and transfer errors. He did use an HP48 with SMI cards in the 90s or early 2000s, mostly for topo. I??ve tried it in my basement, but find the flexi window access to the keys a nuisance. Anyway, the battery compartment has gotten loose and it powers down unexpectedly. The boss settled on Carlson 2006 because he felt it was less buggy than earlier releases, so he stayed with it. Of course it runs on XP.
James Flemming, R.J. Schneider ?? I??m all for replicate data (redundancy), but boss insists as long as the two turns agree within 5? it??s time to move on and keep the field time at a minimum. I can tell you he??s never at a loss for clients.
Dave Lindell ?? I??m going to have to concede your point. At best adding and subtracting are about the same.
Thebionicman ?? I??m not clear on what your procedure was when you set subdivision control (points?). I??ve only worked a few subdivisions, the boss was running the gun and I was new and learning (of course, still am)
Kris Morgan ?? From my limited experience I think what you??re describing sounds like what I know as direct/reverse shots (FD, BD, FR, BR) using both instrument faces. We??ve not done that on any jobs, but I??ve tried it in a basement setup and compared it with forward shots alone. I couldn??t find any statistically significant difference so I wondered why bother so long as you can show a consistent lack of difference. Your comment about the effect of faulty compensation is the first insight I??ve had on that question.
I??ll have to confess that I??m clueless about your last lines:
?ÿ??Especially handy when setting corners and you turn the first angle, get line and distance, flip and turn the exact double and split the holes.?ÿ Double centering makes for really good control to come off of in a pinch.?
Especially the part: ??get line and distance, flip and turn the exact double and split the holes?
Where can I find the details on that? I??ve surveyed my own property, the boss has finalized the drawing and I??m looking to set a lot of corner markers this spring.
HP48 with SMI cards
Thats a calculator, not a data collector. Not rugged enough for survey field work.
That is so funny that my 3 HP48jGX with SMI v7 are laughing and trying to escape their environmental cases.
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All I can say is that most surveying equipment is not necessarily designed for every hand or any hands for matter and to use them repeadly and correctly and fast and accurately requires dedication, adaptation and very little complaining.
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HP48 with SMI cardsThats a calculator, not a data collector. Not rugged enough for survey field work.
It's a data collector, Lee. It's not like he's cutting line with it.
I've been using HP48GX 's for more than 20 years in SMI environmental cases.?ÿ Never once lost data, or lost a day due to dead batteries.?ÿ?ÿ
